Evaluation of Railway Track Substructure Moduli Using Falling Weight Deflectometer Backcalculation

This study evaluates the applicability of Falling Weight Deflectometer (FWD) testing for backcalculating substructure layer moduli in railway tracks using an integrated approach with Dynamic Cone Penetrometer (DCP) and Ground Penetrating Radar (GPR). Field investigations were conducted at 15 locations along the railway at Fort Leonard Wood, Missouri. The railway substructure was modeled as a three-layer system consisting of somewhat loose crib ballast, compacted ballast, and subgrade. DCP measurements were used to define layer interfaces and estimate subgrade modulus, while GPR data supplemented layer thickness evaluations when the subgrade interface could not be identified from the DCP profiles. Two FWD backcalculation approaches were examined: (1) an unconstrained method that estimates moduli for all three layers, and (2) a constrained method that fixes the subgrade modulus using DCP-derived values while estimating only the upper layers. The consistency and reliability of each approach were assessed through statistical analyses and comparison with soil classification data from the United States Department of Agriculture (USDA) Web Soil Survey. Additional analyses examined the relationships between backcalculated ballast modulus, FWD deflection responses, and GPR-derived fouling index. Results demonstrate that integrating FWD, DCP, and GPR provides a comprehensive and reliable framework for evaluating railway substructure conditions.